Collapsing the Hierarchy

As you model, you start off simple, add details until your model is more complex, then collapse the mesh and start on the next level of complexity. Collapsing lets you convert your subdivision changes to polygonal components that can be edited in polygon mode with the polygon tool set. By collapsing the mesh, your model becomes more complex, but you get more editing possibilities.

The Collapse Hierarchy command reduces the number of levels in a subdiv surface. Collapse Hierarchy lets you specify the number of levels you wish to collapse and moves the edits from those levels to the level above.

To collapse subdiv hierarchy:

1.	From the Create menu, select Polygon Primitives > Cube.
2.	Right-click the cube and select Face from the Marking Menu (Figure 9.52). Figure 9.52. Select Face from the Marking menu.
3.	Select a face on one side of the cube (Figure 9.53). Figure 9.53. Select a face.
4.	Right-click the cube and select Refine from the Marking menu (Figure 9.54). Figure 9.54. Select Refine from the Marking menu. This adds a level-1 to the mesh (Figure 9.55). Figure 9.55. By refining the face, you've added a level to the model.
5.	Right-click and select Polygon from the Marking menu. Notice that the polygon cage does not show the detail that was created by adding level-1 (Figure 9.56). Figure 9.56. Polygon mode does not show the added detail of level-1.
6.	From the Subdiv Surfaces menu, select the box next to Collapse Hierarchy. The Subdiv Collapse Options dialog box opens (Figure 9.57). Figure 9.57. Set the Number of Levels to 1 in the Subdiv Collapse Options dialog box.
7.	Set the Number of Levels to 1 and click Apply. A collapsed copy of the selected surface is made (Figure 9.58). Figure 9.58. After applying Collapse Hierarchy, the surface now has the level-1 detail in level-0.
8.	Right-click the cube and select Polygon from the Marking menu (Figure 9.59). Figure 9.59. Select Polygon from the Marking menu. Notice that the polygon cage now shows the detail that was created by adding level-1 and that the overall cage is much more dense (Figure 9.60). Figure 9.60. The new surface allows the detail that was in level-1 to be edited in polygon mode.

Tip

• Maya's Mental Ray Renderer only renders Subdiv Surfaces that are quadralateral. This means that all the faces involved in the mesh may only have four sides. Maya's renderer, however, will render non-quadralateral subdiv surfaces. Collapse Hierarchy will fix non-quad subdivs so that Mental Ray will render them.